The scariest five sentences I read yesterday come from Michael Mandel, Business Week's chief economist and the author of the recent cover story, How Real Was the Prosperity?

In truth, we're at the beginning of a long, arduous process of figuring out how much of the post-tech bubble prosperity was real and how much was the result of a credit-induced frenzy... As of the third quarter of 2007, the 10-year growth rate for consumption was 3.6%, vs. GDP growth for the same period of 2.9%. This difference represents an enormous gap. If consumer spending had tracked the overall economy over the past decade as it has in the past, Americans today would be spending about $600 billion less a year. The extra spending has amounted to a total of about $3 trillion since 2001.

In other words, since the tech bubble really took off in 1997, which was followed by the credit bubble of the early 2000s, which was followed by the housing bubble, consumer spending has outpaced economic growth by $3 trillion. The implication: Such a rate of growth was based on funny stock-market and housing money and is woefully unsustainable. Over the years I have written many columns saying (correctly) that consumers still had gas in the tank and shouldn't be ruled out. Now, seeing the figures as Mandel puts them, and seeing the challenges the economy faces, I think it is probably time to stop saying that.